Process of precipitating silver halide in the presence of a colloid and a water-soluble iron salt

ABSTRACT

A PROCESS FOR PRODUCING A SILVER HALIDE PHOTOGRAPHIC EMULSION INCLUDING A STEP OF PRECIPITATING A SILVER HALIDE IN A COLLOIDAL SOLUTION BY REACTION BETWEEN A HALIDE AND A SILVER SALT, CHARACTERIZED IN THAT SAID PRECIPITATION IS   DONE IN THE PRESENCE OF A WATER-SOLUBLE IRON COMPOUND IN AN AMOUNT OF 10-7 TO 10-3 MOL PER MOL OF THE SILVER SALT CONTAINED IN SAID SOLUTION.

June 27,

DENSITY KINJI OHKUBO ETAL 3,672, 1

PROCESS OF PRECIPITATING SILVER HALIDE IN THE PRESENCE OF A COLLOID ANDA, WATEB SOLQBLE I RON SALT Filed May 15; 1970 l-s 2 0 2-5 3'-0 |0g.EARBITRARY unn (lux. sec.)

INVENTORS KINJI OHKUBO JUNPEI NOGUCHI KUNIOKI OHMURA 6 (7144:, BY z g 1TTORNEYS United States Patent Office Patented June 27, 1972 3,672,901PROCESS OF PRECIPITATING SILVER HALIDE [N THE PRESENCE OF A COLLOID ANDA WATER- SOLUBLE IRON SALT Kinji Ohkubo, Jnnpei Noguchi, and KuniokiOhmura, Kanagawa, Japan, assignors to Fuji Photo Film Co., Ltd.,Kanagawa, Japan Filed May 15, 1970, Ser. No. 37,618 Claims priority,application Japan, May 17, 1969, 44/ 38,249 Int. Cl. G03c 1/02 us. or.96-94 16 Claims ABSTRACT OF THE DISCLOSURE A process for producing asilver halide photographic emulsion including a step of precipitating asilver halide in a colloidal solution by reaction between a halide and asilver salt, characterized in that said precipitation is done in thepresence of a water-soluble iron compound in an amount of to 10- mol permol of the silver salt contained in said solution.

This invention relates to a process for production of a photosensitivephotographic emulsion for use in a silver halide photographic material,and more particularly, to a process for production of a silver halidephotographic emulsion for use in a photographic material which forms ahigh contrast image.

It has hitherto been known that in order to obtain high contrast silverhalide photographic materials, such metal salts as rhodium salts (seeFIAT Final Report No. 360), cobalt-cyano complex salts (see US. patentspecification 2,517,541) or iridium salts (seen Japanese patentpublication No. 4935/68) are added to the solutions employed in makingemulsion preparations. Another process for the preparation of highcontrast silver halide photographic materials is described in US. patentspecification 3,062,647. In this process incorporation of a polyalkyleneoxide and a colloid of a noble metal (silver, gold, platinum, palladium)possibly in conjunction with a colloid of a metal sulfide (silversulfide, zinc sulfide) in a gelatin binder of the silver halidephotographic emulsion, will produce the desired photographic materials.

Of the above-cited metal salts effective for obtaining high contrastimages, the rhodium salts exhibit remarkable eifects on silver chloride,but have the defect of causing a marked desensitization. The iridiumsalts only show a marked effect in obtaining high contrast images withflash exposure in a photographic emulsion prepared by precipitating asilver halide at a pH of less than 6.5. Furthermore, the cobalt-cyanocomplex salts are effec tive on silver chloride, but are toxic andrequire careful handling.

An object of the present invention is to provide a process for producinga silver halide photographic emulsion of high contrast easily andeconomically. This process includes a step of precipitating a silverhalide in a colloidal solution, such as a gelatin solution, by reactionof a halide with a silver salt. This precipitation is done in thepresence of a water-soluble iron compound in an amount of 10* to 10-mols per mol of the silver salt contained in said solution.

The critical featture of the present invention resides in the proportionof the water-solution iron compound to be added to the reaction system.It has unexpectedly been found that the presence of a very small amountof the water-soluble iron compound in the reaction system leads to thepreparation of a photographic emulsion capable of forming a highcontrast photographic image without a marked reduction in sensitivity.

The iron compounds used in the invention are watersoluble divalent ortrivalent iron salts or complex salts.

Specific examples include: ferrous arsenate, ferrous bromide, ferrouscarbonate, ferrous chloride, ferrous citrate, ferrous fluoride, ferrousformate, ferrous gluconate, ferrous hydroxide, ferrous iodide, ferrouslactate, ferrous oxalate, ferrous phosphate, ferrous succinate, ferroussulfate, ferrous thiocyanate, ferrous nitrate, ammonium ferrous sulfate,potassium hexacyanoferrate (II), potassium pentacyanoamine-ferrate (H),basic ferric acetate, ferric albuminate, ammonium ferric acetate, ferricbromide, ferric chloride, ferric chromate, ferric citrate, ferricfluoride, ferric formate, ferric glycero phosphate, ferric hydroxide,acidic ferric phosphate, ferric nitrate, ferric phosphate, ferricpyrophosphate, sodium ferric ethylenedinitrilotetraacetate, sodiumferric pyrophosphate, ferric thiocyanate, ferric sulfate, ammoniumferric sulfate, guanidine ferric sulfate ammonium ferric citrate,potassium hexacyanoferrate (III), tris(dipyridyl) iron (III) chloride,potassium ferric pentacyanonitrosyl, and hexaurea iron (III) chloride.

Of these compounds, hexacyanoferrates (II), hexaeyanoferrates (III), andferric thiocyanate exhibit especially marked effects.

The iron compound described above is added during the formation ofsilver halide particles to a gelatin solu tion, a halide solution, or asilver salt solution. It is also possible to add a separately preparedsolution of the iron compound to a suspension of a silver halide duringthe formation of silver halide particles to a gelatin soluprocedures maybe employed conjointly. In any of the procedures, it is desirable thatan amount of the iron compound to be added is 10* to 10- mol per mol ofsilver present in the silver salt solution. Amounts of the iron compoundbelow 10 mol scarcely show a high contrast image producing effect, whileamounts above 10- mol cause a marked reduction in the photographicsensitivity of the resulting silver halide photographic material.

The silver halide may be silver chloride, silver chlorobromide, silverbromide, silver iodobromide, or silver chloroiodobromide. The use of theiron compound in accordance with the invention is effective for aphotographic emulsion prepared by any of the ammonia, neutral or acidicmethods to produce a high contrast image. The conventionally known highcontrast image producing agents, such as rhodium or iridium salts, maybe added together with the iron compound to obtain an additive highcontrast image forming effect. In conjunction with these, various metalsalts, such as nickel salts, copper salts, zinc salts, cadmium salts,mercury salts, lead salts and thallium salts can also be used to improvethe sensitivity or gradation of the photographic emulsion.

A silver halide suspension obtained in accordance with the process ofthe invention by forming silver halide particles in the presence of aniron compound can be chemically ripened with a usual method.Specifically, the suspension is directly sent to the next chemicalripening step or it is redissolved after setting, shredding, and rinsingwith water. In another method, it is coagulated and precipitated withgelatin and then re-dispersed in a solution of gelatin. In the chemicalripening procedure, a suitable noble metal salt, sulfur sensitizer,reduction sensitizer, etc., are added, and the resulting mixture isheated to raise the sensitivity. As such noble metal salts, gold salts,palladium salts, iridium salts, platinum salts, etc., are known.Furthermore, suitable additives, suchas 3 color sensitizers,anti-foggants, wetting agents, or gelatin hardening agents are added,and the finished emulsion is coated on a support and dried. Photographicmaterials prepared in the absence of an iron compound under the aboveconditions have a lesser contrast than those materials prepared underthese conditions in the presence of '11011. I

A photographic material may also be prepared by adding a developingagent to a gelatin-silver halide photographic emulsion prepared inaccordance with the process of the present invention, or by disposing alayer containing a developing agent adjacent to the emulsion layer. Suchphotographic material is exposed, and developed by contact with analkaline solution (to be referred to as activator treatment). In thiscase also, the presence of an iron compound in the preparation of thephotographic material enhances contrast in the photographic material.

The process of the present invention exhibits an adwantage thatphotographic materials of high contrast can be manufactured readily andat low cost.

The invention will further be described by the following examples whichare intended to be illustrative rather than limitative.

EXAMPLE 1 Solutions (1), (2), '(3) and (4) of the following recipes wereprepared:

Solution (1):

Gelatin: 40 g.

Citric acid: 1.3 g.

Distilled water: 750 g.

Sodium chloride (maintained at 60 C.): 11 g. Solution (2):

A 0.01 wt. percent aqueous solution of potasium hexacyanoferrate (IH): 3cc.

Solution (3):

Silver nitrate: 20 g.

Distilled water (maintained at 58 C.): 150 cc. Solution (4):

Gelatin: 80 g.

Distilled water (maintained at 60 C.): 200 cc.

Solution (1) was stirred in the dark, and solution (2) was addedthereto. Solution (3) was further added over a period of 3 minutes. Theresulting mixed solution was left to stand for minutes, and thensolution (4) was added. The resulting mixed solution was stirred, andripened for 90 minutes at 60 C. After ripening, 24 cc. of a 10 wt.percent aqueous solution of formaldehyde was added to the solution toform a coating solution. The coating solution was applied to barvtapaper to produce a photographic paper. The amount of the silver halidepresent in the resulting emulsion layer was 1.8 g./m. calculated assilver.

A photographic paper was prepared in the same manner as described aboveexcept that solution (2) was not added. This was a comparative specimen,whereas the photographic paper obtained above was a specimen that comeswithin the scope of the invention.

These specimens were exposed for $4 second through an optical wedge, anddeveloped for .30 seconds at 20 C. with a developer solution, Papitol (aphenidonehydroquinone type developing agent for photographic paper,product of Fuji Photo Film, Co., Ltd.), followed by fixing, waterrinsing, and drying treatments. The photographic image obtained from thephotographic material of the invention had a gamma value of 2.28,Whereas the image obtained from the comparative specimen had a gammavalue of 1.95.

The photographic characteristic curves of each of these specimens areshown in the accompanying drawing, in which the reflection density ofthe developed image is plotted against the logarithm of the exposure. Inthe drawing, curve 1 is a characteristic curve of the specimen inaccordance with the invention, while curve 2 is that of the comparativespecimen.

It is seen from both of these curves that the photographic emulsionprepared by the process of the invention is excellent in that itimproves the gradation of the developed image.

EXAMPLE 2 A photographic emulsion was prepared in the same manner as setforth in Example 1 except that 3 cc. of a 0.01 wt. percent aqueoussolution of potassium hexacyanoferrate (H) was used in place of thepotassium hexacyanoferrate (III) as solution (2). A photographic paperwas prepared using the resulting emulsion. The photographiccharacteristics of this specimen were measured in the same way as inExample 1, and the gamma value of the developed image was found to be2.21. Comparison of this specimen with the comparative specimen shown inExample 1 indicates that the emulsion prepared in accordance with theinvention is excellent in photographic properties.

EXAMPLE 3 Solutions (1), (2), (3) and (4) of the following recipes wereprepared.

Solution (1):

Gelatin: 15 g.

Citric acid: 1.3 g.

Distilled water (maintained at 63 C.): 250 cc. Solution (2):

A 0.01 wt. percent aqueous solution of potassium hexacyanoferrate (H1):4 cc.

Solution (3):

Silver nitrate: 25 g.

Distilled water (maintained at 60 C.): 200 cc. Solution (4):

Potassium bromide: 8.8 g.

Sodium chloride: 6.8 g.

Distilled water (maintained at 63 C.): 300 cc.

While stirring solution (1) in the dark, solutions (2), (3) and (4) wereadded simultaneously thereto over a period of 30 minutes. The resultingmixed solution was maintained at 63 C. and left to stand for 5 minutes.With further addition of g. of dry gelatin, the mixture was allowed tostand for 60 minutes, followed by addition of 24 cc. of :a 10 wt.percent aqueous solution of formaldehyde to form a coating solution. Thecoating solution was applied to baryta paper to produce a photographicpaper. The amount of the silver halide present in the resulting emulsionlayer was 2.1 g./rr.l. calculated as silver. A comparative sample [wasprepared in the same way as above except that the solution (2) was notadded.

Both of these specimens were exposed for $4 second through an opticalwedge, and developed for 30 seconds at 20 C. with the Papitol developersolution set forth in Example 1, followed by fixing, water rinsing, anddrying treatments. The photographic properties of both samples wereexamined in the same manner as in Example 1. As a result, it was foundthat the specimen prepared in accordance with the present invention hada gamma value of 1.70, whereas the comparative specimen had a gammavalue of 1.39. This indicates a good elfect of the present invention.

EXAMPLE 4 A photographic paper was prepared in the same manner as setforth in Example 3 except that 4 cc. of a 0.01 wt. percent aqueoussolution of potassium hexacyanofer-rate (II) was used instead of thepotassium hexacyanoferrate (III) as solution (2). The photographic paperwas treated in the same way as in Example 3 to form a photographicimage. The developed image had a gamma value of 1.67.

LEXAM PLE 5 A photographic paper was prepared in the same way as setforth in Example 3 except that 4 cc. of a 0.01 wt.

percent of aqueous solution of ferric thiocyanate was used instead ofthe potassium hexacyanoferrate (III) as solution (2). The photographicpaper was treated in the same way in Example 3 to form a photographicimage. The developed image had a gamma value of 1.60.

EXAMPLE 6 Solutions (.1), (2), (3) and (4) of the following recipes wereprepared.

Solution l Gelatin: 10 g. Potassium iodide: 0.8 g. Aqueous ammonia(ION): 18 cc.

Distilled water (maintained at 48 C.): 430 cc. Solution (2):

A 0.01 wt. percent aqueous solution of potassium hexacyanoferrate (III):7 cc. Solution (3):

Silver nitrate: 80 g. Distilled water (maintained at 45 C.): 300 cc.Solution (4):

Potassium bromide: 33.6 g. Sodium chloride: 16.8 g. Aqueous solution ofammonium rhodium chloride (0.01% by weight): 0.5 cc. Distilled water(maintained at 48 C.): 350 cc.

While stirring solution (1) in the dark, solutions (2), (3) and (4) wereadded simultaneously over a period of 50 minutes. Immediately, sulfuricacid was added to adjust the pH of the mixed solution to 4.5. Thesolution was allowed to stand for 20 minutes at 48 C. With furtheraddition of 110 g. of dry gelatin, the solution was allowed to stand for30 minutes. The resulting emulsion was cooled to gelati'on, shredded,and then washed with cold water for one hour. The emulsion was heated to60 C. to redissolve gelatin, and the pAg value was adjusted to 7.2 byaddition of an aqueous solution of cadmium chloride. With furtheraddition of a sensitizer, 5 cc. of a 0.01 wt. percent aqueous solutionof tetrachloroaurate (III), the emulsion was left to stand for 60minutes, followed by addition of 24 cc. of a wt. percent aqueoussolution of formaldehyde to form a coating solution. The coatingsolution was applied to baryta paper. The amount of the silver halidepresent in the formed emulsion layer was 2.0 g./m. calculated as silver.

A comparative specimen was prepared in the same manner as describedabove except that solution (2) was not added.

These specimens were exposed for second through an optical wedge, anddeveloped for 2 minutes at C. with the Papitol developer describedabove, followed by fixing, water rinsing, and drying treatments. Animage obtained from the specimen of the invention has a gamma value of1.87, whereas that obtained from the comparative specimen had a gammavalue of 1.5-8.

EXAMPLE 7 Two photographic emulsions (specimen of the invention andcomparative specimen) were prepared in the same manner as set forth inExample 6, Hydrochloric acid was added to each of the emulsions toadjust its pH to 4.0. 30 grams of hydroquinone was added per kilogram ofthe emulsion, and 24 cc. of a 10 wt. percent aqueous solution offormaldehyde was added to baryta paper.

These two specimens were exposed for $5 second, and developed andstabilized using a Quick Copy Treating Solution and a Quick IndustrialProcessor (both being the products of Fuji Photo Film Co., Ltd., Japan).An image obtained from the specimen of the invention had a gamma valueof 1.65, whereas that obtained from the comparative specimen had a gammavalue of 1.30.

As is clear from the foregoing examples, the present invention exhibitsexcellent effects in any specific embodi- 6 ments and is very useful inimproving the quality of photographic images.

What is claimed is:

1. A process for producing a silver halide photographic emulsionconsisting essentially of precipitating silver halide particles in acolloidal solution by reacting a silver salt and a halide in thepresence of, during said precipitation step, from 10"" to 10- mole, permole of the silver salt, of a water-soluble iron compound.

2. The process of claim 1 wherein said colloidal solution is produced bymixing separate solutions of said halide, said silver salt and acolloidal material.

3. The process of claim 2 wherein said colloidal material is gelatin.

4. The process of claim 2 wherein said water-soluble iron compound isadded to said solution of said colloidal material prior to said mixingstep.

5. The process of claim 2 wherein said water-soluble iron compound isadded to said halide solution prior to said mixing step.

6. The process of claim 2 wherein said water-soluble iron compound isadded to said silver salt solution prior to said mixing step.

7. The process of claim 1 wherein said silver halide emulsion is agold-sensitized emulsion.

8. The process of claim 1 further comprising adding to said silverhalide photographic emulsion a developing agent and developing theresulting photographic material by contacting said photographic materialwith an alkaline solution.

9. The process of claim 1 wherein said water-soluble iron compound is adivalent or trivalent iron salt or a complex salt of an iron.

10. The process of claim 1 wherein said water-soluble iron compound is ahexacyanoferrate (II), a hexacyanoferrate (III) or a ferric thiocyanate.

11. The process of claim 3 wherein said water-soluble iron compound is ahexacyanoferrate (II), a hexacyanoferrate (III) or ferric thiocyanate.

12. The process of claim 1 wherein said water-soluble iron compound isselected from the group consisting of ferrous arsenate, ferrous bromide,ferrous carbonate, ferrous chloride, ferrous citrate, ferrous fluoride,ferrous formate, ferrous gluconate, ferrous hydroxide, ferrous iodide,ferrous lactate, ferrous oxalate, ferrous phosphate, ferrous succinate,ferrous sulfate, ferrous thiocyanate, ferrous nitrate, ammonium ferroussulfate, potassium hexacyanoferrate (II), potassiumpentacyanoamine-ferrate (II), basic ferric acetate, ferric albuminate,ammonium ferric acetate, ferric bromide, ferric chloride, ferricchromate, ferric citrate, ferric fluoride, ferric formate, ferricglycero-phosphate, ferric hydroxide, acidic ferric phosphate, ferricnitrate, ferric phosphate, ferric pyrophosphate, sodium ferricethylenedinitrilotetraacetate, sodium ferric pyrophosphate, ferricthiocyanate, ferric sulfate, ammonium ferric sulfate, guanidine ferricsulfate, ammonium ferric citrate, potassium hexacyanoferrate (III),tris(dipyridyl) iron (III) chloride, potassium ferricpentacyanonitrosyl, and hexaurea iron (III) chloride.

13. A silver halide photographic emulsion produced by the process ofclaim 1.

14. A process for producing a silver halide photographic emulsionconsisting of precipitating silver halide particles in a gelatinsolution by reacting a silver salt and a halide in the presence of,during said precipitation step, from 10- to 10 mole, per mole of thesilver salt, of a water-soluble iron compound.

15. The process of claim 14 wherein said silver salt is silver nitrate.

16. The process of claim 14 wherein said water-soluble iron compound isa hexacyanoferrate (II), a hexacyano ferrate (III) or ferricthiocyanate.

(References on following page) 7 8 References Cited FOREIGN PATENTSUNITED STATES PATENTS 911,488 11/1962 Great Britain 96114.7

2,540,085 2/1951 Baldsiefen 96-108 I 2,618,556 11/1952 Hewitson 96-414.?5 NORMAN TORCHIIL Pnmary Exammer 3,178,289 4/1965 Sottysiak 96114.7 J.R. HIGHTOWER, Assistant Examiner 3,418,122 12/1968 0011 96-108 3,449,1256/1969 Bigelow 96-108 US. Cl. X.R. 3,531,289 9/1970 Wood 96-94 -11 13,531,291 9/1970 Bacon 96-94 10

